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UCC28600
SLUS646K – NOVEMBER 2005 – REVISED AUGUST 2015
UCC28600 8-Pin Quasi-Resonant Flyback Green-Mode Controller
1 Features
3 Description
•
The UCC28600 is a PWM controller with advanced
energy features to meet stringent world-wide energy
efficiency requirements.
1
•
•
•
•
•
•
•
•
•
Green-Mode Controller With Advanced Energy
Saving Features
Quasi-Resonant Mode Operation for Reduced
EMI and Low Switching Losses (Low-Voltage
Valley Switching)
Low Standby Current for Minimum System NoLoad Power Consumption
Low Start-up Current: 25-μA Maximum
Programmable Line and Load Over-Voltage
Protection
Internal Over-Temperature Protection
Current Limit Protection
– Cycle-by-Cycle Power Limit
– Primary-Side Over-Current Hiccup Restart
Mode
1-A Sink, –0.75-A Source TrueDrive™ Gate Drive
Output
Programmable Soft-Start
Green-Mode Status Pin (PFC Disable Function)
UCC28600 integrates built-in advanced energy
saving features with high-level protection features to
provide cost-effective solutions for energy-efficient
power supplies. UCC28600 incorporates frequency
fold-back and green-mode operation to reduce the
switching losses at light-load and no-load conditions.
UCC28600 is available in the 8-pin SOIC package.
Operating junction temperature range is –40°C to
+105°C.
The UCC28600 Design Calculator, (SLVC104),
located in the Tools and Software section of the
UCC28600 product folder, provides a user-interactive
iterative process for selecting recommended
component values for an optimal design.
Device Information
PART NUMBER
•
•
BODY SIZE (NOM)
SOIC (8)
4.90 mm × 3.91 mm
(1) For all available packages, see the orderable addendum at
the end of the data sheet.
2 Applications
•
PACKAGE
UCC28600
(1)
Bias Supplies for LCD-Monitors, LCD-TV, PDPTV, and Set Top Boxes
AC-to-DC Adapters and Off-Line Battery Chargers
Energy Efficient Power Supplies up to 200 W
Typical Application Diagram
Primary
CBULK
RSU
NP
Secondary
NS
NB
CB
18 V
ROVP1
UCC28600
CSS
1
SS
STATUS
8
CVDD
UCC28051
1
VO_SNS
VCC
8
2
FB
OVP
7
2
COMP
DRV
7
3
CS
VDD
6
3
MULTIN
GND
6
4
GND
OUT
5
4
CS
ZCD
5
ROVP2
Feedback
CBP
M1
RPL
RCS
TL431
1
An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,
intellectual property matters and other important disclaimers. PRODUCTION DATA.
UCC28600
SLUS646K – NOVEMBER 2005 – REVISED AUGUST 2015
www.ti.com
Table of Contents
1
2
3
4
5
6
7
Features ..................................................................
Applications ...........................................................
Description .............................................................
Revision History.....................................................
Pin Configuration and Functions .........................
Specifications.........................................................
1
1
1
2
3
4
6.1
6.2
6.3
6.4
6.5
6.6
6.7
4
4
4
4
5
6
7
Absolute Maximum Ratings ......................................
ESD Ratings ............................................................
Recommended Operating Conditions.......................
Thermal Information ..................................................
Electrical Characteristics...........................................
Timing Requirements ................................................
Typical Characteristics ..............................................
Detailed Description .............................................. 8
7.1 Overview ................................................................... 8
7.2 Functional Block Diagram ......................................... 8
7.3 Feature Description................................................. 11
7.4 Device Functional Modes........................................ 18
8
Application and Implementation ........................ 21
8.1 Application Information............................................ 21
8.2 Typical Application ................................................. 21
8.3 Do's and Don'ts ...................................................... 33
9 Power Supply Recommendations...................... 34
10 Layout................................................................... 34
10.1 Layout Guidelines ................................................. 34
10.2 Layout Example .................................................... 35
11 Device and Documentation Support ................. 36
11.1
11.2
11.3
11.4
11.5
Device Support ....................................................
Documentation Support .......................................
Trademarks ...........................................................
Electrostatic Discharge Caution ............................
Glossary ................................................................
36
36
36
36
36
12 Mechanical, Packaging, and Orderable
Information ........................................................... 37
4 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Revision J (July 2011) to Revision K
Page
•
Added Pin Configuration and Functions section, ESD table, Feature Description section, Device Functional Modes,
Application and Implementation section, Power Supply Recommendations section, Layout section, Device and
Documentation Support section, and Mechanical, Packaging, and Orderable Information section. .................................... 1
•
Changed Functional Block diagram........................................................................................................................................ 8
•
Changed Control Flow Chart diagram .................................................................................................................................. 11
•
Changed QR Detect Details image. ..................................................................................................................................... 13
•
Changed Oscillator Details image. ....................................................................................................................................... 14
•
Changed Fault Logic Details image...................................................................................................................................... 16
•
Changed Mode Control with FB Pin Voltage image. ........................................................................................................... 18
•
Changed Operation Mode Switching Frequencies image. .................................................................................................. 19
Changes from Revision H (November 2005) to Revision I
•
2
Page
Changed Equation 35 .......................................................................................................................................................... 29
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SLUS646K – NOVEMBER 2005 – REVISED AUGUST 2015
5 Pin Configuration and Functions
D Package
8-Pin SOIC
Top View
SS
FB
CS
GND
1
2
3
4
8
7
6
5
STATUS
OVP
VDD
OUT
Pin Functions
PIN
NAME
CS
NO.
3
I/O
DESCRIPTION
I
Current sense input. Also programs power limit, and used to control modulation and activate
overcurrent protection. The CS voltage input originates across a current sense resistor and
ground. Power limit is programmed with an effective series resistance between this pin and
the current sense resistor.
FB
2
I
Feedback input or control input from the optocoupler to the PWM comparator used to control
the peak current in the power MOSFET. An internal 20-kΩ resistor is between this pin and
the internal 5-V regulated voltage. Connect the collector of the photo-transistor of the
feedback optocoupler directly to this pin; connect the emitter of the photo-transistor to GND.
The voltage of this pin controls the mode of operation in one of the three modes: quasi
resonant (QR), frequency foldback mode (FFM) and green mode (GM).
GND
4
–
Ground for internal circuitry. Connect a ceramic 0.1-μF bypass capacitor between VDD and
GND, with the capacitor as close to these two pins as possible.
OUT
5
O
1-A sink (TrueDrive™ ) and 0.75-A source gate drive output. This output drives the power
MOSFET and switches between GND and the lower of VDD or the 13-V internal output
clamp.
OVP
7
I
Over voltage protection (OVP) input senses line-OVP, load-OVP and the resonant trough for
QR turn-on. Detect line, load and resonant conditions using the primary bias winding of the
transformer, adjust sensitivity with resistors connected to this pin.
SS
1
I
Soft-start programming pin. Program the soft-start rate with a capacitor to ground; the rate is
determined by the capacitance and the internal soft-start charge current. The soft-start
capacitor should be placed as close as possible to the SS pin and GND, keeping trace
length to a minimum. All faults discharge the SS pin to GND through an internal MOSFET
with an RDS(on) of approximately 100 Ω. The internal modulator comparator reacts to the
lowest of the SS voltage, the internal FB voltage and the peak current limit.
STATUS
8
O
ACTIVE HIGH open drain signal that indicates the device has entered standby mode. This
pin can be used to disable the PFC control circuit (high impedance = green mode). STATUS
pin is high during UVLO, (VDD < start-up threshold), and softstart, (SS < FB).
I
Provides power to the device. Use a ceramic 0.1-μF by-pass capacitor for high-frequency
filtering of the VDD pin, as described in the GND pin description. Operating energy is usually
delivered from auxiliary winding. To prevent hiccup operation during start-up, a larger energy
storage cap is also needed between VDD and GND.
VDD
6
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SLUS646K – NOVEMBER 2005 – REVISED AUGUST 2015
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6 Specifications
6.1 Absolute Maximum Ratings
over operating free-air temperature range (unless otherwise noted)
(1)
MIN
MAX
UNIT
32
V
Supply current
20
mA
Output sink current (peak)
1.2
A
Output source current (peak)
–0.8
A
–0.3
6.0
V
–1.0
6.0
V
–1.0
mA
VDD
Supply voltage range, IDD < 20 mA
IDD
IOUT(sink)
IOUT(source)
Analog inputs: FB, CS, SS
VOVP
IOVP(source)
VSTATUS
VDD = 0 V to 30 V
30
V
Power dissipation, SOIC-8 package, TA = 25°C
650
mW
TLEAD
Lead temperature 1,6 mm (1/16 inch) from case for 10 seconds
300
°C
TJ
Operating junction temperature
–55
150
°C
Tstg
Storage temperature
–65
150
°C
(1)
Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings
only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended
Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
6.2 ESD Ratings
V(ESD)
(1)
(2)
Electrostatic discharge
VALUE
UNIT
Human body model (HBM), per ANSI/ESDA/JEDEC JS-001, all
pins (1)
±2000
V
Charged device model (CDM), per JEDEC specification
JESD22-C101, all pins (2)
±1500
V
JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
JEDEC document JEP157 states that 250-V CDM allows safe manufacturing with a standard ESD control process.
6.3 Recommended Operating Conditions
over operating free-air temperature range (unless otherwise noted)
MIN
VDD
Input voltage
CVDD
VDD bypass capacitor
CFB
FB filter capacitor
TJ
Operating junction temperature
NOM
MAX
21
0.1
UNIT
V
μF
1.0
–40
390
pF
105
°C
6.4 Thermal Information
UCC28600
THERMAL METRIC
(1)
D (SOIC)
UNIT
8 PINS
RθJA
Junction-to-ambient thermal resistance
108.9
°C/W
RθJC(top)
Junction-to-case (top) thermal resistance
55.5
°C/W
RθJB
Junction-to-board thermal resistance
48.9
°C/W
ψJT
Junction-to-top characterization parameter
10.5
°C/W
ψJB
Junction-to-board characterization parameter
48.5
°C/W
(1)
4
For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report, SPRA953.
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SLUS646K – NOVEMBER 2005 – REVISED AUGUST 2015
6.5 Electrical Characteristics
VDD = 15 V, 0.1-μF capacitor from VDD to GND, 3.3-nF capacitor from SS to GND charged over 3.5 V, 500-Ω resistor from
OVP to –0.1 V, FB = 4.8 V, STATUS = not connected, 1-nF capacitor from OUT to GND, CS = GND, TA = –40°C to +105°C,
(unless otherwise noted)
PARAMETER
TEST CONDITIONS
TYP
MAX
12
25
μA
VFB = 0 V
350
550
μA
Not switching
2.5
3.5
mA
130 kHz, QR mode
5.0
7.0
mA
21
26
32
V
ISTARTUP
Start-up current
VDD = VUVLO –0.3 V
ISTANDBY
Standby current
IDD
Operating current
VDD clamp
FB = GND, IDD = 10 mA
MIN
UNIT
UNDERVOLTAGE LOCKOUT
VDD(uvlo)
Start-up threshold
VDD increasing
10.3
13.0
15.3
V
VDD(uvlo)
Stop threshold
VDD decreasing
6.3
8
9.3
V
ΔVDD(uvlo)
Hysteresis
4.0
5.0
6.0
V
PWM (RAMP)
(1)
DMIN
Minimum duty cycle
VSS = GND, VFB = 2 V
DMAX
Maximum duty cycle
QR mode, fS = max, (open loop)
0%
99%
OSCILLATOR (OSC)
fQR(max)
Maximum QR and DCM frequency
fQR(min)
Minimum QR and FFM frequency
VFB = 1.3 V
fSS
Soft start frequency
VSS = 2.0 V
dTS/dFB
VCO gain
TS for 1.6 V < VFB < 1.8 V
117
130
143
kHz
32
40
48
kHz
32
40
48
kHz
–38
–30
–22
μs/V
12
20
28
kΩ
FEEDBACK (FB)
RFB
Feedback pullup resistor
VFB
FB, no load
QR mode
3.30
4.87
6.00
V
Green-mode ON threshold
VFB threshold
0.3
0.5
0.7
V
Green-mode OFF threshold
VFB threshold
1.2
1.4
1.6
V
Green-mode hysteresis
VFB threshold
0.7
0.9
1.1
V
FB threshold burst-ON
VFB during green mode
0.3
0.5
0.7
V
FB threshold burst-OFF
VFB during green mode
0.5
0.7
0.9
V
Burst Hysteresis
VFB during green mode
0.13
0.25
0.42
V
RDS(on)
STATUS on resistance
VSTATUS = 1 V
1.0
2.4
3.8
kΩ
ISTATUS(leakage)
STATUS leakage/off current
VFB = 0.44 V, VSTATUS = 15 V
2.0
μA
STATUS
(1)
–0.1
RCST and CCST are not connected in the circuit for maximum and minimum duty cycle tests, current sense tests, and power limit tests.
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Electrical Characteristics (continued)
VDD = 15 V, 0.1-μF capacitor from VDD to GND, 3.3-nF capacitor from SS to GND charged over 3.5 V, 500-Ω resistor from
OVP to –0.1 V, FB = 4.8 V, STATUS = not connected, 1-nF capacitor from OUT to GND, CS = GND, TA = –40°C to +105°C,
(unless otherwise noted)
PARAMETER
CURRENT SENSE (CS)
ACS(FB)
VCS(os)
VPL
MIN
TYP
MAX
UNIT
Gain = ΔVFB / ΔVCS
QR mode
Shutdown threshold
VFB = 2.4 V, VSS = 0 V
1.13
1.25
1.38
V
CS discharge impedance
CS = 0.1 V, VSS = 0 V
25
115
250
Ω
CS offset
SS mode, VSS ≤ 2.0 V
0.35
0.40
0.45
V
CS current
OVP = –300 μA
–165
–150
–135
μA
Peak CS voltage
QR mode
0.70
0.81
0.92
V
PL threshold
Peak CS voltage + CS offset
1.05
1.20
1.37
V
POWER LIMIT (PL)
IPL(cs)
TEST CONDITIONS
(1)
2.5
V/V
(1)
SOFT START (SS)
ISS(chg)
Softstart charge current
VSS = GND
–8.3
–6.0
–4.5
μA
ISS(dis)
Softstart discharge current
VSS = 0.5 V
2.0
5.0
10
mA
VSS
Switching ON threshold
Output switching start
0.8
1.0
1.2
V
–450
–370
μA
–25
mV
OVERVOLTAGE PROTECTION (OVP)
IOVP(line)
Line overvoltage protection
IOVP threshold, OUT = HI
–512
VOVP(on)
OVP voltage at OUT = HIGH
VFB = 4.8 V, VSS = 5.0 V,
IOVP(on), = –300 μA
–125
VOVP(load)
Load overvoltage protection
VOVP threshold, OUT = LO
3.37
3.75
4.13
V
130
140
150
°C
THERMAL PROTECTION (TSP)
Thermal shutdown (TSP)
temperature (2)
Thermal shutdown hysteresis
(2)
15
°C
Ensured by design. Not production tested.
6.6 Timing Requirements
CURRENT SENSE (CS)
MIN
NOM
MAX
UNIT
100
175
300
ns
50
100
150
ns
(1)
CS to output delay time (power limit), CS = 1.0 VPULSE
CS to output delay time (over current fault), CS = 1.45 VPULSE
OUT
tRISE
Rise time, 10% to 90% of 13-V typical OUT clamp
50
75
ns
tFALL
Fall time
10
20
ns
(1)
6
RCST and CCST are not connected in the circuit for maximum and minimum duty cycle tests, current sense tests, and power limit tests.
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31
142
29
137
fS – Switching Frequency – kHz
VDD – Clamp Voltage – V
6.7 Typical Characteristics
27
25
23
21
–50
132
127
122
117
0
50
100
150
–50
0
TJ – Temperature – °C
Figure 1. Clamp Voltage vs. Temperature
100
150
Figure 2. Switching Frequency vs. Temperature
-372
IOVP Over-Voltage Protection Threshold - PA
0.95
PL Threshold, QR Mode, Peak CS Voltage – V
50
TJ – Temperature – °C
0.90
0.85
0.80
0.75
-392
-412
-432
-452
-472
-492
0.70
–50
0
50
100
150
-512
-50
TJ – Temperature – °C
0
50
100
150
TJ - Temperature - °C
Figure 3. PL Threshold vs. Temperature
Figure 4. Over-Voltage Protection Threshold vs.
Temperature
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UCC28600
SLUS646K – NOVEMBER 2005 – REVISED AUGUST 2015
www.ti.com
7 Detailed Description
7.1 Overview
The UCC28600 is a flyback power supply controller that operates in different operating modes, modulating the
peak primary current and/or the switching frequency, depending upon the line and load conditions. The controller
will operate in burst mode operation, or green mode (GM) driving the primary side MOSFET with packets of
40-kHz pulses, at fixed peak primary current for light-load conditions. As the load increases, the 40-kHz switching
will become consistent and the controller will transition to frequency fold-back mode (FFM), where the peak
primary current is held constant and the switching frequency is modulated from 40 kHz up to 130 kHz, in order to
maintain regulation. At higher loads, the UCC28600 will operate in either DCM, where the peak primary current is
modulated but the switching frequency is maintained at its maximum value, or quasi-resonant mode (QRM),
where the switching frequency and the peak primary current are both modulated in order to maintain regulation.
7.2 Functional Block Diagram
RSU
CBULK
RVDD
CVDD
ROVP1
OVP
VDD
ROVP2
6
7
UCC28600
REF
+
VDD_OK
5.0
VREF
26 V
ILINE
13/8 V
On-Chip
Thermal
Shutdown
STATUS
Fault Logic
REF_OK
VDD_OK
OVR_T
LOAD_OVP
STATUS
LINE_OVP
SS_DIS
CS
SS_MODE
BURST
RUN
8
VREF
6PA
SS
QR DETECT
____
LOAD_OVP OUT
LINE_OVP
CS
BURST
QR_DONE
OSCILLATOR
RUN
SS_MODEQR_DONE
1
CSS
OSC_CL
REF
D
CLK
+
FB
2
Q
Modulation
Comparison
3
RPL
ILINE
2
RCS
+
R
VCS(os)
4
GND
+
1.5R
OUT
CS
GAIN = 1/2.5
20 k:
5
Q
PL
1.2 V
REF
Feedback
SET
CLR
GREEN MODE
OSC_CL
FB
FB_CLAMP
VDD
400 mV
8
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Functional Block Diagram (continued)
7.2.1 Terminal Components
Table 1. Terminal Components
PIN
NAME
NO.
I/O
DESCRIPTION
V
PL
RCS
ICS(2) IP(1) ICS(1) IP(2)
V
PL
RPL
VCS(os) IP(2) IP(1)
(1)
ICS(1) IP(2) ICS(2) IP(1)
(2)
I
where:
•
IP(1) is the peak primary current at low line, full load (2)
•
IP(2) is the peak primary current at high line, full load (2)
•
ICS(1) is the power limit current that is sourced at the CS pin at low-line voltage (2)
•
ICS(2) is the power limit current that is sourced at the CS pin at high-line voltage (2)
•
VPL is the Power Limit (PL) threshold (1)
•
VCS(os) is the CS offset voltage (1)
2
I
Opto-isolator collector
4
–
Bypass capacitor to VDD, CBP = 0.1 μF
5
O
Power MOSFET gate
CS
3
FB
GND
OUT
OVP
VCS(os) ICS(2) ICS(1)
(1) (2)
7
I
ROVP1
§ NB
·
1
VBULK(ov) ¸
¨
IOVP(line) © NP
¹
ROVP2
§
·
¨
¸
VOVP(line)
¸
ROVP1 ¨
¨ NB V
¸
OUT(shutdown) VF VOVP(load) ¸
¨N
© P
¹
(3)
(4)
where:
•
IOVP(line) is OVPline current threshold (1)
•
VBULK(ov) is the allowed input over- voltage level (2)
•
VOVP(load) is OVPload (1)
•
VOUT(shutdown) is the allowed output over-voltage level (2)
•
VF is the forward voltage of the secondary rectifier
•
NB is the number of turns on the bias winding (2)
•
NS is the number of turns on the secondary windings (2)
•
NP is the number of turns on the primary windings (2)
CSS ! ISS u
tSS(min) duepower limit
ACS(FB) u VPL VCS(os)
(5)
where tSS(min) is the greater of:
tSS(min)
ª RLOAD(ss)COUT
VOUT 'VOUT(step) º
ln
«
»
2
RLOAD(ss)POUT(max)limit ¼»
¬«
(6)
ª COUT VOUT 2 º
«
»
«¬ 2PLIM
»¼
(7)
or
SS
1
I
tSS(min)
•
•
•
•
•
•
•
(1)
(2)
RLOAD(ss) is the effective load impedance during soft-start (2)
ΔVOUT(step) is the allowed change in VOUT due to a load step
POUT(max limit) Programmed power limit level, in W (2)
ACS(FB) is the current sense gain (1)
VCS(os) is the CS offset voltage (1)
ISS is the soft-start charging current (1)
VPL is the power limit threshold (1)
(2)
Refer to the Electrical Characteristics for constant parameters.
Refer to the UCC28600 Design Calculator (SLVC104) or laboratory measurements for currents, voltages and times in the operational
circuit.
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Functional Block Diagram (continued)
Table 1. Terminal Components (continued)
PIN
NAME
NO.
I/O
DESCRIPTION
RST2
RST1
STATUS
8
O
(1) (2)
VBE(off )
ISTATUS(leakage)
(8)
ª
§ I ·º
RST2 u « VDD(uvlo on) VBE(sat) RDS(on) u ¨ CC ¸ » RDS(on) VBE(sat)
«¬
© Esat ¹ »¼
§ § ICC ·
·
u RST2 ¸ VBE(sat)
¨¨ ¨ Esat ¸
¸
¹
©©
¹
(9)
where:
•
βSAT is the gain of transistor QST in saturation
•
VBE(sat) is the base-emitter voltage of transistor QST in saturation
•
VDD(uvlo-on) is the start-up threshold (1)
•
ICC is the collector current of QST
•
ISTATUS(leakage) is the maximum leakage/off current of the STATUS pin (1)
•
VBE(off) is the maximum allowable voltage across the base emitter junction that will not turn QST on
•
RDS(on) is the RDS(on) of STATUS (1)
CVDD is the greater of:
ª
TBURST º
« IDD CISS VOUT(hi) fQR(max)
»
'VDD(burst) ¼»
¬«
(10)
C VDD
ª
º
TSS
« IDD CISS VOUT(hi) fQR(max)
»
'VDD(uvlo) »¼
«¬
(11)
R VDD
§
·
§ S · § NB · ¨ VDS1(os) fQR(max) LLEAKAGE CD CSNUB ¸
¨ 4 ¸¨ N ¸¨
¸
IDD
C
V
f
© ¹© P ¹
ISS OUT(hi) QR(max)
©
¹
(12)
C VDD
or
RSU
VDD
10
6
I
VBULK(min)
(13)
ISTARTUP
where:
•
IDD is the operating current of the UCC28600 (1)
•
CISS is the input capacitance of MOSFET M1
•
VOUT(hi) is VOH of the OUT pin, either 13 V (typ) VOUT clamp or less as measured
•
fQR(max) is fS at high line, maximum load (1)
•
TBURST is the measured burst mode period
•
ΔVDD(burst) is the allowed VDD ripple during burst mode
•
ΔVDD(uvlo) is the UVLO hysteresis (1)
•
VDS1(os) is the amount of drain-source overshoot voltage
•
LLEAKAGE is the leakage inductance of the primary winding
•
CD is the total drain node capacitance of MOSFET M1
•
ISTARTUP is IDD start-up current of the UCC28600 (1)
•
CSNUB is the snubber capacitor value
•
tSS is the soft start charge time (2)
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7.3 Feature Description
The UCC28600 is a multi-mode controller, as illustrated in Figure 5 and Figure 12. The mode of operation
depends upon line and load conditions. Under all modes of operation, the UCC28600 terminates the OUT = HI
signal based on the switch current. Thus, the UCC28600 always operates in current mode control so that the
power MOSFET current is always limited.
Under normal operating conditions, the FB pin commands the operating mode of the UCC28600 at the voltage
thresholds shown in the control flow chart, Figure 11. Soft-start and fault responses are the exception. During
soft start, the converter switching frequency is fixed at 40 kHz and FB is set to 5V. The soft-start mode is
latched-OFF when VSS becomes greater than VFB for the first time after UVLOON. The soft-start state cannot be
recovered until after passing UVLOOFF, and then, UVLOON.
From 100% to approximately 30% full rated power the UCC28600 controls the converter in quasi-resonant mode
(QRM) or discontinuous conduction mode (DCM), where DCM operation is at the clamped maximum switching
frequency (130 kHz). For loads that are between approximately 30% and 10% full rated power, the converter
operates in frequency foldback mode (FFM), where the peak switch current is constant and the output voltage is
regulated by modulating the switching frequency for a given and fixed VIN. Effectively, operation in FFM results in
the application of constant volt-seconds to the flyback transformer each switching cycle. Voltage regulation in
FFM is achieved by varying the switching frequency in the range from 130 kHz to 40 kHz. For extremely light
loads (below approximately 10% full rated power), the converter is controlled using bursts of 40-kHz pulses.
START
Y
RUN = 0
STATUS = 1
N
VCC > 13 V?
Y
RUN = 1
STATUS = 1
VCC < 8 V?
N
REF < 4 V?
OVP = 1?
OT = 1?
OC = 1?
RUN = 0
Soft Start
Monitor VFB
N
VFB < 1.4 V
1.4 V < VFB < 2.0 V
2.0 V < VFB
Fixed V-sec
40 kHz
STATUS = 0
(In Run-Mode)
STATUS = 0
(In Run-Mode)
VFB < 0.5 V
Fixed V-sec
Freq. Foldback
(Light Load)
Quasi-Resonant
Mode or DCM
(Normal Load)
Y
Zero Pulses
STATUS = 1
(In Green-Mode)
STATUS = 0
(In Run-Mode)
Fixed V-sec
40 kHz Burst
N
Y
N
VFB > 1.4 V
Y
VFB > 0.7 V
Y
VFB > 0.5 V
N
Figure 5. Control Flow Chart
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Feature Description (continued)
Details of the functional boxes in the Block Diagram/Typical Application drawing are shown in Figure 8, Figure 6,
Figure 7 and Figure 10. These figures conceptualize how the UCC28600 executes the command of the FB
voltage to have the responses that are shown in Figure 11, Figure 5 and Figure 12. The details of the functional
boxes also conceptualize the various fault detections and responses that are included in the UCC28600. During
all modes of operation, this controller operates in current mode control. This allows the UCC28600 to monitor the
FB voltage to determine and respond to the varying load levels such as heavy, light or ultra-light.
Quasi-resonant mode and DCM occurs for feedback voltages VFB between 2.0 V and 4.0 V, respectively. In turn,
the CS voltage is commanded to be between 0.4 V and 0.8 V. A cycle-by-cycle power limit imposes a fixed 0.8-V
limit on the CS voltage. An overcurrent shutdown threshold in the fault logic gives added protection against highcurrent, slew-rate shorted winding faults, shown in Figure 10. The power limit feature in the QR DETECT circuit
of Figure 7 adds an offset to the CS signal that is proportional to the line voltage. The power limit feature is
programmed with RPL, as shown in the Typical Application Diagram.
Mode Clamps
1.4 V
OSC_CL
+
450 kΩ
+
100 kΩ
FB
2.0 V
450 kΩ
100 kΩ
+
FB_CL
Figure 6. Mode Clamp Details
12
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CIN
RSU
NP
CVDD
Auxiliary
Winding
ROVP1
NS
COUT
NB
ROVP2
VDD
OVP
7
UCC28600
QR Detect
0.1 V
+
Slope
RCS
+
QR_DONE
(Oscillator)
-0.1 V
OUT (From Driver)
0.1 V
+
+
+
REF (5 V)
ILINE
REF (5 V)
Power Limit
Offset
RPL
ILINE
2
1
3.75 V
ILINE
Burst
(from FAULT logic)
LOAD_OVP
(Fault Logic)
+
1 k:
LINE_OVP
(Fault Logic)
0.45 V
0
CS
CS
3
Figure 7. QR Detect Details
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7.3.1 Oscillator
The oscillator, shown in Figure 8, is internally set and trimmed so it is clamped by the circuit in Figure 8 to a
nominal 130-kHz maximum operating frequency. It also has a minimum frequency clamp of 40 kHz. If the FB
voltage tries to drive operation to less than 40 kHz, the converter operates in green mode.
REF
+
OSC Peak
Comparator
4.0V
SS_MODE
S
Q
R
Q
QR_DONE
CLK
+
OSC_CL
0.1V
130 kHz OSC
Clamp
Comparator
+
OSC Valley
Comparator
RUN
Figure 8. Oscillator Details
14
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7.3.2 Status
The STATUS pin is an open drain output, as shown in Figure 10. The status output goes into the OFF-state
when FB falls below 0.5 V and it returns to the ON-state (low impedance to GND) when FB rises above 1.4 V.
This pin is used to control bias power for a PFC stage, as shown in Figure 9. Key elements for implementing this
function include Q1, RST1 and RST2, as shown in Figure 9. Resistors RST1 and RST2 are selected to saturate Q1
when it is desirable for the PFC to be operational. During green mode, the STATUS pin becomes a high
impedance and RST2 causes Q1 to turn-OFF, thus saving bias power. If necessary, use a Zener diode and a
resistor (DZ1 and RVCC) to maintain VCC in the safe operating range of the PFC controller.
NOTE
The DVDD – CVDD combination is in addition to the standard DBIAS – CBIAS components.
This added stage is required to isolate the STATUS circuitry from the start-up resistor, RSU, to ensure there is no
conduction through STATUS when VDD is below the UVLO turn-on threshold.
Primary
CBULK
NP
RSU
Secondary
NS
DBIAS
To Zero
Current
Detection
RVCC
Q1
NB
DVDD
CBIAS
RST2
RST1
10 V
DZ1
UCC28600
UCC28051
VCC
STATUS
M2
8
Feedback
8
M1
2
CVDD
FB
VDD
CVCC
0.1 mF
4
6
RCS
GND
TL431
GND
5
Figure 9. Using STATUS for PFC Shut-Down During Green Mode
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7.3.3 Fault Logic
Advanced logic control coordinates the fault detections to provide proper power supply recovery. This provides
the conditioning for the thermal protection. Line overvoltage protection (line OVP) and load OVP are
implemented in this block. It prevents operation when the internal reference is below 4.5 V. If a fault is detected
in the thermal shutdown, line OVP, load OVP, or REF, the UCC28600 undergoes a shutdown/retry cycle.
Refer to the fault logic diagram in Figure 10 and the QR detect diagram in Figure 7 to program line OVP and load
OVP. To program the load OVP, select the ROVP1 – ROVP2 divider ratio to be 3.75 V at the desired output shutdown voltage. To program line OVP, select the impedance of the ROVP1 – ROVP2 combination to draw 450 μA
when the VOVP is 0.45 V during the ON-time of the power MOSFET at the highest allowable input voltage.
UCC28600
REF
VDD_OK
REF_OK
SET
D
Q
OVR_T
CLR
Thermal
Shutdown
REF
(5 V)
Q
RUN
LINE_OVP (QR
Detect)
SS/DIS
LOAD_OVP
(QR Detect)
20 kW
S
Q
R
Q
BURST
+
0.6 V/0.7 V
FB
1.25 V
+
Burst
Power-Up Reset
8
STATUS
7
0.6 V/1.5 V
FB
+
SS_MODE
CS
3
CS
Figure 10. Fault Logic Details
16
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7.3.4 Protection Features
The UCC28600 has many protection features that are found only on larger, full featured controllers. Refer to the
Functional Block Diagram, Typical Application Diagram, Figure 6, Figure 7, Figure 8, Figure 10, Figure 11, and
Figure 12 for detailed block descriptions that show how the features are integrated into the normal control
functions.
7.3.5 Overtemperature
Overtemperature lockout typically occurs when the substrate temperature reaches 140°C. Retry is allowed if the
substrate temperature reduces by the hysteresis value. Upon an overtemperature fault, CSS on softstart is
discharged and STATUS is forced to a high impedance.
7.3.6 Cycle-by-Cycle Power Limit
The cycle terminates when the CS voltage plus the power limit offset exceeds 1.2 V.
In order to have power limited over the full line voltage range of the QR Flyback converter, the CS pin voltage
must have a component that is proportional to the primary current plus a component that is proportional to the
line voltage due to predictable switching frequency variations due to line voltage. At power limit, the CS pin
voltage plus the internal CS offset is compared against a constant 1.2-V reference in the PWM comparator. Thus
during cycle-by-cycle power limit, the peak CS voltage is typically 0.8 V.
The current that is sourced from the OVP pin (ILINE) is reflected to a dependent current source of ½ ILINE, that is
connected to the CS pin. The power limit function can be programmed by a resistor, RPL, that is between the CS
pin and the current sense resistor. The current, ILINE, is proportional to line voltage by the transformer turns ratio
NB/NP and resistor ROVP1. Current ILINE is programmed to set the line over voltage protection. Resistor RPL results
in the addition of a voltage to the current sense signal that is proportional to the line voltage. The proper amount
of additional voltage has the effect of limiting the power on a cycle-by-cycle basis. Note that RCS, RPL, ROVP1 and
ROVP2 must be adjusted as a set due to the functional interactions.
7.3.7 Primary Current Protection
When the primary current exceeds maximum current level which is indicated by a voltage of 1.25 V at the CS
pin, the device initiates a shutdown. Retry occurs after a UVLOOFF or UVLOON cycle. Because the device will
initiate cycle-by-cycle power limit first, primary side current protection is not intended to protect against output
short circuit conditions. However, this feature does protect the MOSFET against extreme conditions such as
transformer saturation.
7.3.8 Over-Voltage Protection
Line and load over voltage protection is programmed with the transformer turn ratios, ROVP1 and ROVP2. The OVP
pin has a 0-V voltage source that can only source current; OVP cannot sink current.
Line over voltage protection occurs when the OVP pin is clamped at 0 V. When the bias winding is negative,
during OUT = HI or portions of the resonant ring, the 0-V voltage source clamps OVP to 0 V and the current that
is sourced from the OVP pin is mirrored to the Line_OVP comparator and the QR detection circuit. The
Line_OVP comparator initiates a shutdown-retry sequence if OVP sources any more than 450 μA.
Load-over voltage protection occurs when the OVP pin voltage is positive. When the bias winding is positive,
during demagnetization or portions of the resonant ring, the OVP pin voltage is positive. If the OVP voltage is
greater than 3.75 V, the device initiates a shutdown. Retry occurs after a UVLOOFF or UVLOON cycle.
7.3.9 Undervoltage Lockout
Protection is provided to guard against operation during unfavorable bias conditions. Undervoltage lockout
(UVLO) always monitors VDD to prevent operation below the UVLO threshold.
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7.4 Device Functional Modes
Depending upon the line and load conditions, the UCC28600 controls the converter using different modes of
operation, which are defined as quasi-resonant (QR mode), discontinuous conduction mode (DCM), frequency
foldback mode (FFM) and green mode (GM), determined by the voltage on the FB pin, as shown in Figure 11.
For extremely light loads (below approximately 10% full rated power), the converter is controlled using bursts of
40-kHz pulses. As the load increases, the number of pulses in these burst packets increases until the converter
is switching consistently at 40 kHz, at which point it transitions into the next operating mode, called frequency
foldback. Frequency foldback mode (FFM) typically begins at loads that are between approximately 10% and up
to 30% full rated power, the peak primary side switch current is constant and the output voltage is regulated by
modulating the switching frequency from 40 kHz up to 130 kHz. From approximately 30% to 100% full rated
power, the UCC28600 controls the converter in either quasi-resonant mode (QRM) or discontinuous conduction
mode (DCM). In QRM, the switching frequency will decrease as the load increases; DCM operation is at the
clamped maximum switching frequency (130 kHz). The valley detection circuitry is active during FFM, DCM, and
QRM operation.
Internal Reference
VFB Control Range Limit
40 kHz < fS < 130 kHz
Green Mode-OFF,
Burst-ON
Green Mode-ON,
Burst-OFF
Keep in mind that the aforementioned boundaries of steady-state operation are approximate because they are
subject to converter design parameters.
FFM
Green Mode
QR Mode or DCM Mode
Green Mode
Hysteresis
Burst
Hysteresis
VFB
0V
0.5 V 0.7 V
1.4 V
2.0 V
4.0 V
5.0 V
Figure 11. Mode Control with FB Pin Voltage
18
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IC Off Softstart
Regular Operation
Fixed Frequency
Frequency Foldback
DCM
(maximum fs)
Constant Voltseconds (ZCS)
Burst Mode
Load Power
POUT
POUT, MAX
t
Switching
Frequency
fsw
fSS
(40 kHz)
SS Mode
(fixed fSW)
QR Mode
(ZVS)
Burst Mode
fMAX = Oscillator
Frequency
(130 kHz)
This mode applies bursts of
40kHz soft-start pulses to the
power MOSFET gate. The
average fsw is shown in this
operating mode.
fGRMODE_MX
(40 kHz)
fQR_MIN : (internally
limited to 40 kHz.
t
Hysteretic
transition into
Burst Mode.
Feedback
Voltage
VFB
t
Power Supply
Output Voltage
VOUT
Status, pulled up
to VDD
t
VSTATUS
Green Mode,
PFC bias OFF
Peak MOSFET
Current
t
Load Shown is slightly less
than Over Current Threshold
t
Figure 12. Operation Mode Switching Frequencies
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7.4.1 Quasi-Resonant and DCM Control
During this control mode, the rising edge of OUT will occur just after the valley of the resonant ring when the
transformer is fully demagnetized. Resonant valley switching is an integral part of QR operation. In this mode, the
flyback converter operates at the boundary of discontinuous conduction mode and continuous conduction mode.
By adjusting both the peak current and the switching frequency, the output power is adjusted to match the load
requirement. When the load increases, the peak current increases and the switching frequency decreases. The
minimum switching frequency of the converter is limited to 40 kHz. The transformer magnetizing inductor value
has to be designed accordingly so that the converter can deliver the maximum required power while maintaining
a switching frequency that is greater than the fQR(min) over the entire input operating range.
As the load decreases from its designed maximum output power, the UCC28600 will demand a higher switching
frequency and decreased peak current. The converter’s maximum switching frequency will be limited to 130 kHz.
At this maximum switching frequency, the converter enters DCM control. At DCM control, the peak current is
adjusted to control the output power. Slight frequency dithering between resonant valleys will occur as the valley
detection is active in DCM control.
Quasi-resonant (QR) and DCM operation occur for feedback voltages, VFB, between 2.0 V and 3.0 V. In turn, the
peak CS voltage is commanded to be between 0.4 V and 0.8 V. The CS pin has an internal dependent current
source, 1/2 ILINE. This current source adds a proportional step offset (power limit offset) to the CS signal and is
part of the cycle-by-cycle power limit function that is discussed in the Protection Features section.
7.4.2 Frequency Foldback Mode Control
Operation in FFM results in the application of constant volt-seconds to the flyback transformer during each
switching cycle. During frequency foldback mode, as the load decreases, the MOSFET peak current is kept
constant and the switching frequency is reduced (foldback) to reduce the output power. In this mode, the flyback
converter will always operate in discontinuous conduction mode. When the FB voltage is between 1.4 V and
2.0 V, the voltage controlled oscillator restricts the operating frequency between 40 kHz and 130 kHz and the CS
is clamped to 0.4 V, including the power limit offset. Valley detection is active during FFM.
7.4.3 Green-Mode Control
During green mode, the converter operates at a fixed switching frequency of 40 kHz and fixed peak current. The
output power is adjusted by the converter ON/OFF durations, which is also known as burst mode. When the FB
voltage is between 1.4 V and 0.5 V, the controller is commanding an excess of energy to be transferred to the
load which in turn, drives the error higher and FB lower. When FB reaches 0.5 V, the OUT pulses are terminated
and do not resume until FB reaches 0.7 V. In this mode, the converter operates in hysteretic control with the
OUT pulse terminated at a fixed CS voltage level of 0.4 V. The power limit offset is turned OFF during Green
mode and it returns to ON when FB is above 1.4 V. Green mode reduces the average switching frequency in
order to minimize switching losses and increase the efficiency at light-load conditions.
7.4.4 Operating Mode Programming
Boundaries of the operating modes are programmed by the flyback transformer and the four components RPL,
RCS, ROVP1 and ROVP2; shown in the Functional Block Diagram and Typical Application Diagram drawing.
The transformer characteristics that predominantly affect the modes are the magnetizing inductance of the
primary and the magnitude of the output voltage, reflected to the primary. To a lesser degree (yet significant), the
boundaries are affected by the MOSFET output capacitance and transformer leakage inductance. The design
procedure here is to select a magnetizing inductance and a reflected output voltage that operates at the
DCM/CCM boundary at maximum load and maximum line. The actual inductance should be noticeably smaller to
account for the ring between the magnetizing inductance and the total stray capacitance measured at the drain
of the power MOSFET. This programs the QR/DCM boundary of operation. All other mode boundaries are preset
with the thresholds in the oscillator and green-mode blocks.
The four components RPL, RCS, ROVP1 and ROVP2 must be programmed as a set due to the interactions of the
functions. The use of the UCC28600 design calculator, SLVC104, is highly recommended in order to achieve the
desired results with a careful balance between the transformer parameters and the programming resistors.
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8 Application and Implementation
NOTE
Information in the following Applications section is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers
are responsible for determining suitability of components for their purposes.
Customers should validate and test their design implementation to confirm system
functionality.
8.1 Application Information
The UCC28600 device is a flyback controller that operates in a mode that is determined by the FB voltage. Line
and load conditions set the FB voltage and the controller will operate in Green Mode (GM) under light-load
conditions, Frequency Foldback Mode (FFM) when operating at loads approximately between 10% and 30% full
rated load, and Quasi-Resonant (QR) or Discontinuous Mode (DCM) at higher loads. Valley switching under all
modes, except green mode, reduces switching losses and improves efficiency. Valley skipping also helps reduce
EMI. A dedicated STATUS pin is used in higher power applications that use a power factor corrected (PFC) front
end. Under light-load conditions, the STATUS signal can be used to disconnect the bias power to the PFC
controller, reducing light-load power consumption.
8.2 Typical Application
A typical application for the UCC28600 is an off-line flyback controller from 65 W to 120 W, using a PFC output
voltage as its input, as shown in Figure 13. The PFC stage is assumed to operate from a universal AC input and
can be controlled by a device such as the UCC28051. The auxiliary winding provides the bias to the controllers
and provides over voltage protection and valley switching information, as well as bias to the UCC28600 and
UCC28051. The UCC28600 will disable the PFC controller during green mode operation, improving light-load
system efficiency. The series resistor connected between the current sense pin and the current sense resistor
programs the power limit of the converter. Low valley voltage switching and multi-mode operation will keep the
efficiency curve high over the entire operation range. Typical applications include bias supplies for LCD monitors,
LCD and PDP televisions, set top boxes, AC-DC adaptors, and energy efficient power supplies up to 200 W.
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Typical Application (continued)
PFC OUTPUT
or
BRIDGE RECTIFIER
PRIMARY
+
CBULK
RSU
RSNUB
CSNUB
N1
VBULK
SECONDARY
+
N2
COUT
-
D2
RVDD
CVDD
PFC CONTROLLER BIAS
(if used)
QST
VOUT
ROUT
-
D1
NB
CBIAS
ROVP1
RST2
ICC
RST1
UCC28600
1
SS
STATUS
8
2
FB
OVP
7
3
CS
VDD
6
4
GND
OUT
5
CSS
FEEDBACK
ROVP2
M1
TL431
CBP
100nF
RPL
RCS
Figure 13. Simplified Application
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Typical Application (continued)
8.2.1 Design Requirements
The following table illustrates a typical set of performance requirements for an off-line flyback converter.
Table 2. Design Example Performance Requirements
PARAMETER
VIN
AC line input voltage
fLINE
Line frequency
PFCOUTPUT
PFC output voltage
PFC
Input power factor
CONDITIONS
Input to PFC stage
MIN
NOM
MAX
UNIT
85
115/230
265
VRMS
47
50/60
63
Hz
350
390
400
V
VIN = 115 VRMS, IOUT = 6.2 A
0.998
VIN = 230 VRMS, IOUT = 6.2 A
0.97
VOUT
Output voltage
85 VRMS ≤ VIN ≤ 265 VRMS,
0 A ≤ IOUT ≤ 6.2 A
19.0
IOUT
Output load current
85 VRMS ≤ VIN ≤ 265 VRMS
0
VRIPPLE
Output voltage ripple
85 VRMS ≤ VIN ≤ 265 VRMS,
IOUT = 6.2 A
250
mV
VOVP
Output over voltage limit
VIN = 115 VRMS, IOUT = 6.2 A
23.4
V
VIN = 230 VRMS, IOUT = 6.2 A
23.6
V
fCO
19.4
19.8
V
6.2
A
Control loop bandwidth
VIN = 115 VRMS, IOUT = 3 A
2.6
kHz
Phase margin
VIN = 115 VRMS, IOUT = 3 A
70
degrees
ηPEAK
Peak efficiency
VIN = 265 VRMS, IOUT = 6 A
87.4%
η
Full load efficiency
VIN = 115 VRMS, IOUT = 6.2 A
82.7%
VIN = 230 VRMS, IOUT = 6.2 A
86.4%
No load power consumption
VIN = 115 VRMS, IOUT = 0 A
230
mW
VIN = 230 VRMS, IOUT = 0 A
420
mW
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8.2.2 Detailed Design Procedure
This procedure outlines the steps to design an off-line universal input quasi-resonant flyback converter using the
UCC28600. Refer to Figure 13 for component names and network locations. For additional design help, the
design calculator, SLVC104, provides a user-interactive iterative process for selecting recommended component
values for an optimum design when used without a PFC input.
8.2.2.1 Input Bulk Capacitor and Minimum Bulk Voltage
Bulk capacitance may consist of one or more capacitors connected in parallel, often with some inductance
between them to suppress differential-mode conducted noise. EMI filter design is beyond the scope of this
design procedure.
The minimum bulk valley voltage, VBULK(min) is dependent upon the input CBULK capacitor value; this minimum
valley voltage is used in the power stage design. The input capacitor is chosen to maintain an acceptable input
voltage ripple. For a design that uses a regulated PFC output voltage for the input rail the required input
capacitor to the flyback stage is calculated using the minimum PFC output voltage, VPFCoutput(min). Assuming a
15% ripple, the desired minimum bulk valley voltage is:
VBULK(min) = 0.85 x VPFCoutput(min)
(14)
Designs that do not have a PFC input stage will require a much larger input capacitor. The VBULK(min) when
designing without a PFC input stage will be based upon the allowable voltage at the valley of the ripple on the
input rail, which can be 25% to 40% of the minimum rectified AC line voltage. Under those conditions, substitute
the value of the minimum rectified line voltage for VPFCoutput(min) and the value of the maximum rectified line
voltage wherever VPFCoutput(max) is used.
The maximum input power, PIN, is estimated by the output power, POUT, and full-load efficiency target, η, as
shown:
POUT VOUT u IOUT max
PIN max
(15)
The following equation provides an accurate solution for determining the input capacitance needed to achieve
the minimum bulk valley voltage target, VBULK(min):
CBULK
ª
§ VBULK min · º
1
¸»
2PIN u «0.25
u arcsin ¨
«
2
¨ 9PFCoutput min ¸ »
©
¹¼
¬
t
2
2
VPFCoutput min VBULK min u fLINE min
(16)
If an input capacitance other than the calculated value is used, iterate the VBULK(min) value until the desired
capacitance is obtained so that the actual VBULK(min) is determined.
24
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8.2.2.2 Transformer Turns Ratio and Primary Inductance
The allowable flyback voltage, VFLYBACK, seen by the MOSFET, determines the minimum primary to secondary
turns-ratio, NPS. The flyback voltage is calculated based upon the acceptable Drain to Source voltage rating of
the MOSFET and the maximum PFC output voltage rail, VPFCoutput(max) (or rectified maximum line voltage if not
using a PFC input stage), and derating to account for voltage spikes due to leakage inductance:
VFLYBACK
V
DS max
VPFCoutput max
1.5
(17)
Typically, in an off-line design or a design with a PFC output voltage of 390 VDC to 400 VDC, a MOSFET rated
for VDS(max) of 600 VDS or greater is used. The primary to secondary turns-ratio takes the output diode voltage
drop, VF, into account:
VFLYBACK
NPS
VOUT VF
(18)
The primary to bias winding turns ratio is calculated, based upon the desired bias voltage, VBIAS, for the
UCC28600 controller and the PFC controller bias voltage, making sure to avoid the absolute maximum rating for
VDD of each controller:
V
NPB NPS u OUT
VBIAS
(19)
The switching frequency at the minimum bulk valley voltage is used as a limiting factor for the maximum primary
inductance. The UCC28600 will operate in quasi-resonant mode during operation at maximum load, minimum
input voltage and its peak primary current and its switching frequency will be modulated during each switching
cycle. Using a switching frequency of 80 kHz, for fSW, at this operating point will give adequate margin for
manufacturing tolerances in the transformer, the parasitic switch node capacitance, which influences the
resonant frequency to each valley, and keep the controller from trying to go continuous during transient
conditions. The switching period, tSW, is equal to 1/fSW. Using volt-second balance, the maximum primary
inductance can be calculated:
2
LP max
ªV
u VOUT VF u NPS u 0.925 u tSW º
fSW
« BULK min
» u
«
»
2 u PIN max
VBULK min NPS u VOUT VF
¬
¼
(20)
The resistor divider on OVP senses the line voltage during the switch on-time when the auxiliary winding voltage
is proportional to the line voltage. During this portion of the switching cycle, the OVP pin is internally clamped to
approximately 0 V and sources current proportional to the line voltage. The ROVP1 resistor is chosen using the
nominal line over-voltage protection current threshold, IOVP(line), which is equal to 450 µA.
VBULK OVP
ROVP1
NPB u IOVP line
(21)
The OVP pin is also used to sense the output voltage when the OUT signal is low. To set the output overvoltage level, VOUT(shutdown), which is the desired voltage level on the output that would cause the controller to
shutdown, use the load overvoltage protection threshold, VOVP(load), equal to 3.75 V, to determine the required
ROVP2 resistor.
ROVP1 u VOVP load
ROVP 2
NPS
u VOUT shutdown VF VOVP load
NPB
(22)
The peak primary current at low input voltage, full load, IP(1), can be estimated with the following equation:
VBULK min u VOUT VF u NPS u 0.925 u tSW
IP 1
N u V
V
L u V
P
BULKmin
PS
OUT
F
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The switching frequency at maximum input voltage can be estimated:
fSWvin max
2
2
2
NPS
uVPFCoutput
max u 0.925 u VOUT VF
2
2 u LP u PINmax u ªVPFCoutput max NPS u VOUT VF º
«¬
»¼
2
(24)
Now that the switching frequency at the maximum input voltage has been determined, the peak primary current
at maximum load, IP(2), at the maximum input voltage can be calculated:
ª
0.925 º
»
VPFCoutput max u «NPS u VOUT VF u
fSWvin max »
«
¬
¼
IP 2
ª
º
LP u NPS u VOUT VF VPFCoutput max
¬«
¼»
(25)
The power limit current that is sourced at the CS pin adds a voltage step to the CS waveform that is proportional
to the line voltage. At minimum input voltage, maximum load, this current is referred to as ICS(1) and can be
estimated from the following equation:
ICS 1
ª
§ 1
1 · VBULK min º
»
0.5 u «550mV u ¨
¸
© ROVP1 ROVP 2 ¹ NPB u ROVP1 ¼»
¬«
(26)
At maximum input voltage and maximum load, the power limit current sourced from CS is referred to as ICS(2) and
is estimated using the same formula:
ICS 2
ª
§ 1
1 · VPFCoutput max º
»
0.5 u «550mV u ¨
¸
«¬
© ROVP1 ROVP 2 ¹ NPB u ROVP1 »¼
(27)
The appropriate values of the current sense resistor, RCS, and the power limit resistor, RPL, are both dependent
upon the internal power limit threshold, VPL = 1.20 V, the CS offset voltage, VCS(os) = 0.40 V, peak primary
currents, and the power limit currents, calculated above, and can be calculated as shown:
RCS
V V u I I
I u I I u I
V V u I I
I u I I u I
PL
CS 2
RPL
26
CS os
CS 2
CS 1
P 1
CS 1
P 2
PL
CS os
P 2
P 1
CS 1
P 2
CS 2
P 1
(28)
(29)
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8.2.2.3 Non-Ideal Current Sense Value
Resistors RCS, RPL, ROVP1 and ROVP2 must be programmed as a set due to functional interactions in the
converter. Often, the ideal value for RCS is not available because the selection range of current sense resistors is
too coarse to meet the required power limit tolerances. This issue can be solved by using the next larger
available value of RCS and use a resistive divider with a Thevenin resistance that is equal to the ideal RPL value
in order to attenuate the CS signal to its ideal value, as shown in Figure 14. The equations for modifying the
circuit are:
RCS
RPL1 RPL u
RDCS
where
•
•
RDCS = ideal, but non-standard, value of current sense resistor.
RPL = previously calculated value of the power limit resistor.
(30)
RPL1
§ RCS ·
¨
¸ 1
© RDCS ¹
RPL2
where
•
RCS = available, standard value current sense resistor.
(31)
The board should be laid out to include RPL2 in order to fascillitate final optimization of the design based upon
readily available components.
From power
MOSFET
From power
MOSFET
RPL
To CS
RPL1
To CS
RDCS
RPL2
(a)
RCS
(b)
Figure 14. Modifications to Fit a Standard Current Sense Resistor Value
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8.2.2.4 Snubber Damping
Resonance between the leakage inductance and the MOSFET drain capacitance can cause false load-OVP
faults, in spite of the typical 2-μs delay in load-OVP detection. The bias winding is sensitive to the overshoot and
ringing because it is well coupled to the primary winding. A technique to eliminate the problem is to use an R2CD
snubber instead of an RCD snubber, shown in Figure 15. A damping resistor added to the RCD snubber reduces
ringing between the drain capacitor and the inductance when the snubber diode commutates OFF.
PRIMARY
SECONDARY
LLEAK CD
Resonance
+
VIN
CBULK
VD
LM
RSNUB1
'VSNUB
CSNUB
-
VBULK
LLEAK
DS
VR
CD
M1
+
VD
+
VG
0V
-
VG
RCS
0V
(a)
(b)
PRIMARY
+
VIN
-
Reduced LLEAK CD
Resonance
SECONDARY
VD
CBULK
RSNUB2
RSNUB1
'VSNUB
LM
VBULK
CSNUB
LLEAK
DS
VR
CD
M1
+
0V
VD
+
VG
-
VG
0V
RCS
(d)
(c)
Figure 15. (a) RCD Snubber, (b) RCD Snubber Waveform, (c) R2CD Snubber, (d) R2CD Snubber
Waveform
28
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Begin the design of the R2CD using the same procedure as designing an RCD snubber. Then, add the damping
resistor, RSNUB2. The procedure is as follows:
'V
Pick SNUB between0.5and1
VR
(32)
Select a capacitor for ΔVSNUB:
CSNUB
ICS(peak)2LLEAK
VR 'VSNUB 2 VR2
(33)
Pick RSNUB to discharge CSNUB:
§1
VR · 1 § LLEAKICS(peak) ·
RSNUB ¨
¨
¸
¸
© 2 'VSNUB ¹ CSNUB © 'VSNUB
¹
é
é
ùù
ê
ê
úú
DVSNUB ö ê æ 1 ö
1
æ
ú
ê
ú
V
1
+
´
+
´
ç R
1 úú
2 ÷ø ê èç 3 ø÷ ê VR
è
+
ê
êë VSNUB 2 úû ú
ë
û
P (RSNUB1 ) =
RSNUB1
(34)
2
2
(35)
Pick RSNUB2 to dampen the LLEAK-CSNUB resonance with a Q that is between 1.7 and 2.2:
§ 'V
·
RSNUB2 ¨ SNUB ¸
¨ ICS(peak) ¸
©
¹
P RSNUB
(36)
ª
º
«
»
L
f
1
LEAK S(max) »
ICS(peak)2RSNUB2 «
'VSNUB · »
«3 §
¸»
« ¨ VR
2
¹¼
¬ ©
(37)
For the original selection of ΔVSNUB,
Q
2VR
1
'VSNUB
(38)
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8.2.2.5 Open Loop Test Circuit
RCST 37.4k,
See note
CCST 560 pF,
See note
+
5V
UCC28600
1
SS
STATUS
V(FB)
STATUS
8
CSS
3.3 nF
ROVP
500
2
FB
OVP
7
3
CS
VDD
6
4
GND
OUT
5
IOVP
V(OVP)
CFBT
47 pF
V(CS)
ICS
GND
IDD
V(OUT)
CDD
100 nF
CBIAS
1 PF
VDD
ROUT
10
COUT
1.0nF
Figure 16. Open Loop Test Circuit
NOTE
RCST and CCST are not connected for maximum and minimum duty cycle tests, current
sense tests and power limit tests.
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8.2.3 Application Curves
The following figures show the UCC28600 in various operating modes in a 120-W converter, output voltage
equal to 19.4 V.
Drain
CH1: 200 V/
div.
Drain
CH1: 200 V/div.
Gate
CH1: 10 V/div.
Gate
CH2: 10 V/div.
FB
CH1: 1.0 V/div.
FB
CH3: 1.0 V/div.
CS
CH1: 500 mV/
div.
CS
CH4: 500 mV/div.
t - Time - 25 Ps/div.
t - Time - 200 Ps/div.
Figure 17. Green Mode Showing Frequency of Burst
Packets, 900 Hz Apart, 3% Full-Rated Load
Figure 18. Green Mode Showing 40-kHz Switching Within
Burst Packets, 3% Full-Rated Load
Drain
CH1: 200 V/
div.
Drain
CH1: 200 V/
div.
Gate
CH2:10 V/div.
Gate
CH2:10 V/div.
FB
CH3:5.0 V/div.
FB
CH3:5.0 V/div.
CS
CH4:1.0 V/div.
CS
CH4:1.0 V/div.
t - Time - 2.50 Ps/div.
t - Time - 2.50 Ps/div.
Figure 19. Frequency Foldback Mode, 115-kHz Switching,
24% Full-Rated Load
Figure 20. DCM Operation, 130-kHz Switching,
74% Full-Rated Load
25
Drain
CH1: 200 V/
div.
VOUT - Output Voltage - V
20
Gate
CH2: 10 V/div.
FB
CH3: 5.0 V/div.
15
10
CS
CH4: 1.0 V/div.
5
0.0
t - Time - 2.50 Ps/div.
0.0
2
4
6
8
10
12
IOUT - Output Current - A
Figure 21. QR Operation, 116-kHz Switching,
90% Full-Rated Load
Figure 22. Output Voltage vs. Output Current
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120
25
100
Phase
20
80
15
60
10
40
5
20
0
0
-5
100
80
Efficiency - %
30
Phase - O
Gain - dB
SLUS646K – NOVEMBER 2005 – REVISED AUGUST 2015
60
40
-20
Gain
-10
-40
-15
-60
-20
20
-80
1E + 02
1E + 03
1E + 04
0
0.5
1.5
2.5
3.5
4.5
5.5
IOUT - Output Load - A
f - Frequency - Hz
Figure 23. Phase/Gain vs. Frequency
32
VIN = 85VRMS
VIN = 115VRMS
VIN = 230VRMS
VIN = 265VRMS
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Figure 24. Efficiency vs. Output Load
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8.3 Do's and Don'ts
Always be sure to do the following:
• Isolate the STATUS pin from the start up resistor with a diode to prevent the bias current from the bulk input
rail from being diverter away from VDD and into STATUS circuit.
• Use a bypass capacitor on VDD, minimum value of 0.1 µF, to filter high frequency noise.
• Use a large bulk capacitor on VDD to hold the bias above the UVLO turn off threshold between the long
periods of time between burst packets at light load.
• Use a large enough capacitor on SS to prevent triggering power limit when charging the output capacitor
bank at turn on.
• Place the SS capacitor as close as possible to the SS pin with short traces and return to the quiet signal
ground.
• Design the loop crossover frequency to be between 2 kHz to 3 kHz at nominal input voltage and 50% load
with a phase margin of 70 degrees to satisfactorily stabilize the loop for the entire range of operation.
• Add a small filter capacitor to CS to effectively create an RC low pass filter in conjunction with the power limit
resistor, RPL, which will improve noise immunity at the current sense pin.
• Place a 10-kΩ resistor between the gate of the MOSFET and ground to discharge the gate capacitance and
protect against inadvertent dv/dt triggered turn-on.
• Use a small value gate drive resistor in series with the gate drive to control the turn on transition time and
reduce the dv/dt ringing in this node.
• Select the ROVP1, ROVP2, RPL, and RCS together as the OVP resistors set up an internal dependent current
source that impact the RCS and RPL component values.
• Design the transformer so the bias winding is well coupled to both the primary winding and the secondary
winding. The bias winding is used not only for VDD bias but also for valley detection, line over-voltage, load
over-voltage, and power limit off-set current.
CAUTION
Do not use a filter capacitor larger than 390 pF on the FB pin, this capacitor will
provide a delay time to over-load response; capacitors larger than 390 pF will
adversely affect performance.
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9 Power Supply Recommendations
The UCC28600 is intended for AC-to-DC adaptors with input voltage range of 85 VAC(rms) to 265 VAC(rms) using
the flyback topology. This controller can be used in supplies from a few Watts of power up to 200 Watts limited
only by the practical use of a DCM flyback in regards to peak currents and output capacitor component size.
The UCC28600 can be used in bias supplies for LCD monitors, TVs, and set-top boxes, as well as AC-to-DC
adapters for energy-efficient supplies.
10 Layout
10.1 Layout Guidelines
To increase the reliability and feasibility of the design it is recommended to adhere to the following guidelines for
PCB layout.
1. Minimize the high current loops to reduce parasitic capacitances and inductances. At the same time, do not
inadvertently make traces with a high dv/dt too wide as this will create a very good E-field antenna.
2. Separate the device signal ground from the high current power ground in order to isolate the noise away
from the device substrate. The separate grounds should, ideally, be tied together at the input capacitor on
the primary side.
3. Return the sense resistor to the ground side of the input capacitor, instead of to the ground plane under the
device.
4. The bypass capacitor on VDD must be placed as close as possible to the VDD and GND pins of the device.
5. The filter capacitor on CS must be placed as close as possible to the CS pin and GND pin of the device.
6. The filter capacitor on FB must be placed as close as possible to the FB and GND pins of the device.
34
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10.2 Layout Example
The partial layout example shown in Figure 25 demonstrates an effective component and track arrangement for
the printed circuit board. Actual board layout must conform to the constraints on a specific design, so many
variations are possible.
CFB
ROVP2
CSS
SS
STATUS
FB
OVP
ROVP1
UCC28600
CS
VDD
RVDD
GND
OUT
RSU
CVDD3
CCS
To AUX
Winding
RG
RPL
To PGND
To VBULK
G
D
S
RCS
RGS
To PGND
To PGND
CBULK
To PRI
Winding
To VBULK
Figure 25. Partial Layout Example Showing Component Placement
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11 Device and Documentation Support
11.1 Device Support
11.1.1
Development Support
UCC28600 Design Calculator, A QR Flyback Designer.xls, spreadsheet for Microsoft Excel 2003, (SLVC104)
11.2 Documentation Support
11.2.1 Related Documentation
• Power Supply Seminar SEM-1400 Topic 2: Design And Application Guide For High Speed MOSFET Gate
Drive Circuits, by Laszlo Balogh, (SLUP169)
• Datasheet, UCC3581 Micro Power PWM Controller, (SLUS295)
• Datasheet, UCC28051 Transition Mode PFC Controller, (SLUS515)
• Design Considerations for the UCC28600, (SLUA399)
11.2.2 Related Products
• UCC28051 Transition Mode PFC Controller (SLUS515)
• UCC3581 Micro Power PWM Controller (SLUS295)
11.3 Trademarks
TrueDrive is a trademark of Texas Instruments.
All other trademarks are the property of their respective owners.
11.4 Electrostatic Discharge Caution
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
11.5 Glossary
SLYZ022 — TI Glossary.
This glossary lists and explains terms, acronyms, and definitions.
36
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12 Mechanical, Packaging, and Orderable Information
The following pages include mechanical, packaging, and orderable information. This information is the most
current data available for the designated devices. This data is subject to change without notice and revision of
this document. For browser-based versions of this data sheet, refer to the left-hand navigation.
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PACKAGE OPTION ADDENDUM
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13-Aug-2021
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
(4/5)
(6)
UCC28600D
ACTIVE
SOIC
D
8
75
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
-40 to 105
28600D
UCC28600DG4
ACTIVE
SOIC
D
8
75
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
-40 to 105
28600D
UCC28600DR
ACTIVE
SOIC
D
8
2500
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
-40 to 105
28600D
UCC28600DRG4
ACTIVE
SOIC
D
8
2500
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
-40 to 105
28600D
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
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